Evaporators are already widely known which comprise a plurality of flat hollow bodies arranged in parallel and each composed of a pair of dishlike plates facing toward each other and brazed to each other along peripheral edges thereof, a refrigerant inlet header and a refrigerant outlet header arranged side by side in the front-rear direction, and a refrigerant circulating passage for holding the two headers in communication with each other therethrough, the inlet header having a refrigerant inlet at one end thereof, the outlet header having a refrigerant outlet at one end thereof alongside the inlet end, the refrigerant inlet and outlet being formed by making two through holes in the outer plate of the flat hollow body at one end, a refrigerant being permitted to flow from the refrigerant inlet into the inlet header and to return to the outlet header through the circulating passage so as to be sent out from the refrigerant outlet.
With such an evaporator, a joint plate having a short tubular refrigerant inlet portion in communication with the refrigerant inlet and a short tubular refrigerant outlet portion in communication with the refrigerant outlet is joined to the outer plate of the end hollow body so as to face both the inlet header and the outlet header. One end of a refrigerant inlet pipe is inserted into and joined to the refrigerant inlet portion, and a refrigerant outlet pipe having a larger diameter than the inlet pipe has its one end inserted into and joined to the refrigerant outlet portion. The center of the inlet portion of the joint plate is positioned at the same level as the center of the outlet portion thereof. The known joint plate has a short circuit preventing slit formed between the inlet and outlet portions and extending from the upper end or lower end of the plate (see, for example, the publication of JP-A No. 2001-241881). The slit is adapted to prevent short-circuiting between the inlet header and the outlet header in the event of a fault occurring in the brazing joint at the portion of the joint plate between the inlet and outlet portions thereof and the portion between the inlet and the outlet of the flat hollow body. In the event of short-circuiting, the refrigerant admitted through the refrigerant inlet pipe flows into the refrigerant outlet pipe without flowing through the circulating passage, failing to contribute to refrigeration in any way and resulting in seriously impaired refrigeration performance.
It is required in recent years to compact the air conditioner evaporator to be disposed inside vehicle compartments and also to reduce the dimension thereof in the front-rear direction. To diminish the front-to-rear dimension, it is required that the front-to-rear length of the joint plate disclosed in the above publication be decreased, for example, to not larger than 50 mm, whereas in this case, the short circuit preventing slit can not always be provided. If the joint plate disclosed in the publication is made smaller in the front-to-rear length, there is a need to reduce the spacing between the refrigerant inlet portion and the refrigerant outlet portion and to reduce the width of the short circuit prevent slit. However, since the short circuit preventing slit in the joint plate of the publication is formed by press work, the lower limit to the slit width is restricted, and the slit can not be made if the inlet portion and the outlet portion are spaced apart by a small distance.
Accordingly, it appears feasible to individually make an inlet joint plate having a refrigerant inlet portion communicating with the refrigerant inlet of the inlet header and an outlet joint plate having a refrigerant outlet portion communicating with the refrigerant outlet of the outlet header and to join the inlet joint plate to the inlet header and the outlet joint plate to the outlet header. This nevertheless results in an increased number of components, entailing the problem that the joint plates will not be efficiently incorporated into the evaporator to be fabricated.
An object of the present invention is to overcome the above problem and to provide a semifinished joint plate for readily affording a joint plate which is reliably adapted to prevent short-circuiting between the refrigerant inlet header of a heat exchanger and the refrigerant outlet header thereof and which permits the joint plate to be incorporated, with an improved efficiency, into the heat exchanger to be fabricated, the object of the invention further being to provide the joint plate, a process for fabricating the joint plate, and the heat exchanger.